A prior art XY table is constructed as shown in FIG. 4. In the same drawing, a base is indicated by 30, on which a guide rail 31 installed in the X-axis direction and a guide rail 32 installed at the end portion of the guide rail 31 in the Y-axis direction are provided on the base 30. An X-axis table is indicated by 33, which is placed on the guide rail 31 movably in the X-axis direction, and two guide rollers 34 and 35 are attached on the X-axis table 33. An X-axis drive motor is indicated by 36, and an X-axis feed screw 37 having a ball screw is connected to the rotating shaft on the X-axis drive motor 36. A ball nut (not illustrated) attached to the rear side of the X-axis table 33 is screwed in the X-axis feed screw 37, whereby the X-axis table 33 is driven to move in the X-axis direction by rotations of the X-axis feed screw 37. A Y-axis table 38 is placed on the guide rail 32 and attached thereon so as to be movable in the Y-axis direction, and a guide rail 39 extending in the X-axis direction is laid on the Y-axis table 38. A Y-axis drive motor is indicated by 40, and a Y-axis feed screw 41 having a ball screw is connected to the rotating shaft of the Y-axis drive motor, wherein a ball nut (not illustrated) attached on the rear side of the Y-axis table 38 is screwed in the Y-axis feed screw 41, and the Y-axis table 38 is constructed so as to be moved in the Y-axis direction by rotations of the Y-axis feed screw 41. A top table is indicated by 42, in which a groove 43 extending in the Y-axis direction is provided at one side of the top table 42, and one guide roller 34 secured at the X-axis table 33 is brought into contact with the side of the top table 42 while the other guide roller 35 is inserted into the groove 43.
Next, a description is given of the actions of the XY table. As the X-axis drive motor 36 is driven, the X-axis table 33 moves in the X-axis direction via the ball screw of the X-axis feed screw 37 connected to the axis end of the rotating shaft of the X-axis drive motor 36, and at the same time, the top table 42 moves in the X-axis direction via the guide rollers 34 and 35 secured on the X-axis table 33. Next, as the Y-axis drive motor 40 is driven, the Y-axis table 38 moves in the Y-axis direction via the ball screw of the Y-axis feed screw connected to the axis end of the Y-axis drive motor 40. As the Y-axis table 38 moves in the Y-axis direction, the top table 42 on the guide rail 39 laid on the Y-axis table moves in the Y-axis direction integral with the Y-axis table. As the top table 42 moves in the Y-axis direction, the guide rollers 34 and 35 of the X-axis table 33 cause the top table 42 to move and stop at an appointed position while sliding along the side of the top table 42 or in the groove 43.
However, the prior art XY table connects the ball screws attached to the rear side of the X-axis table 33 and Y-axis table 38 to the ball screws of the X-axis feed screw 37 and Y-axis feed screws 41 each connected to the X-axis drive motor 36 and the Y-axis drive motor 40 and cause the X-axis table 33 and the Y-axis table 38 to move. Therefore, it is not possible for the X-axis table 33 and the Y-axis table 38 to be accurately positioned due to errors in screw connection between the ball screw and ball nut. Further, it is not possible for the X-axis table 33 and Y-axis table 38 to move at high-speed acceleration and deceleration by a speed limitation of the ball screws. Therefore, the top table 42, which moves in compliance with the X-axis table 33 and Y-axis table 38 cannot be accurately positioned. Also, the top table 42 cannot be moved at high-speed acceleration and deceleration.